In blow molding machines for stretch-blow molding plastic containers, the container is typically formed from a preform and shaped to a container by means of compressed air. In stretch-blow molding machines, it is common to work with pneumatically or electrically driven stretching systems. This means that a preform is stretched by means of a stretching unit which is operated pneumatically or electrically. Here, the pneumatic/electric stretching cylinders of the stretching unit are frequently pressed onto a curved path. The shape of this curve determines and controls the motion sequence, i.e. the path of a piston in the stretching cylinder. In particular, the pressure in the stretching cylinder and thus the applied force for stretching can be checked thereby, and a maximum stretching power can be adjusted. Such a method is prior art. For example, U.S. Pat. No. 5,866,175 shows a stretch-blow molding machine with a corresponding control system. Several blow molding stations are arranged on a rotating wheel. The stretching process is carried out at the stations. The stretching process is controlled by compressed air. Such systems, however, require a considerable amount of compressed air which is normally consumed. There are ideas to at least partially reuse/recycle the compressed air, so that the consumption of air is reduced, but can often not be eliminated.
As an alternative, there are also systems, such as completely mechanical systems, where a circulating cam, for example a control rail, permanently guides the stretching systems. While no additional air is required, such machines often tend to strong vibrations due to the mechanical coupling which can be normally hard. Moreover, a completely circulating mechanical cam, i.e. complete mechanical guidance of the stretching unit, is very difficult to realize and often failure-prone. Furthermore, it is difficult to realize quick stretching speeds in such a system. The circulating cam, in particular a completely circulating cam unit/rail unit, moreover aggravates the accessibility to the machine.